This research looks at the strength of the R.O.K.-U.S. alliance coherence intensity and the critical junctures that affected South Korean security conditions, and identifies these as the key variables of R.O.K. military power building. Results of the analysis show that as the critical juncture was increasingly related to North Korea and as the R.O.K.-U.S. alliance coherence intensity was strengthened, military power of South Korea was constructed more as a personnel-intensive force structure type. In contrast, it is evident that as the critical juncture was increasingly related to potential threats and as the R.O.K.-U.S. alliance coherence intensity was weakened, military power was constructed more as a technology-intensive force structure type. Considering the uncertainty in future security conditions and the R.O.K.-U.S. alliance, South Korea cannot continue to depend on its ally for national security. It must understand that “Koreanization of South Korea’s defense” is no longer an option. Keeping in mind the security conditions and future warfare, South Korea should prioritize a technology-intensive force structure in order to achieve self-reliance. Because the complex process of building a force structure of this type requires significant investment of time and resources, it must be initiated as early as possible. However, it is important to note that such improvement should not be accompanied by unilateral reduction of troops brought by the lack of consideration for current security conditions. Especially with the possible collapse of North Korea in the future, maintaining sizeable personnel may be critical. Therefore, estimating the size of personnel required and preparing accordingly in advance will be necessary. In conclusion, what South Korea needs most in terms of military power building is a balanced understanding of each category. The country needs a balanced and objective view regarding threats and alliances and balance between public sentiment and economic factors. Therefore, the South Korean military must pursue methods of military power building that do not focus on single issues, but those that consider a balance of multiple long-term factors at the same time, such as alliances, public opinion, and economic factors.